Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of related numbers of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic, such as chloride (Cl−), or organic, such as acetate (C2H3O2−); and can be monatomic, such as fluoride (F−), or polyatomic, such as sulfate (SO42−).

There are several varieties of salts. Salts that hydrolyze to produce hydroxide ions when dissolved in water are basic salts, whilst those that hydrolyze to produce hydronium ions in water are acidic salts. Neutral salts are those that are neither acid nor basic salts. Zwitterions contain an anionic centre and a cationic centre in the same molecule, but are not considered to be salts. Examples include amino acids, many metabolites, peptides, and proteins.

Usually, non-dissolved salts at standard temperature and pressure are solid, but there are exceptions (see Molten salts and ionic liquids).

Molten salts and solutions containing dissolved salts (e.g., sodium chloride in water) are called electrolytes, as they are able to conduct electricity. As observed in the cytoplasm of cells, in blood, urine, plant saps and mineral waters, mixtures of many different ions in solution usually do not form defined salts after evaporation of the water. Therefore, their salt content is given for the respective ions.

Colour


Salts can appear to be clear and transparent (sodium chloride), opaque, and even metallic and lustrous (iron disulfide). In many cases, the apparent opacity or transparency are only related to the difference in size of the individual monocrystals. Since light reflects from the grain boundaries (boundaries between crystallites), larger crystals tend to be transparent, while the polycrystalline aggregates look like white powders. Most minerals and inorganic pigments, as well as many synthetic organic dyes, are salts. The color of the specific salt is due to the presence of unpaired electrons in the d-orbital of transition elements.
 * Salts exist in many different colors, for example:
 * yellow (sodium chromate)
 * orange (potassium dichromate)
 * red (potassium ferricyanide)
 * mauve (cobalt chloride hexahydrate)
 * blue (copper sulfate pentahydrate, ferric hexacyanoferrate)
 * purple (potassium permanganate)
 * green (nickel chloride hexahydrate)
 * colorless (sodium chloride, magnesium sulfate heptahydrate)—may appear white when powdered or in small pieces

The name of a salt starts with the name of the cation (e.g.,  sodium or  ammonium) followed by the name of the anion (e.g.,  chloride or  acetate). Salts are often referred to only by the name of the cation (e.g.,  sodium salt or  ammonium salt) or by the name of the anion (e.g.,  chloride salt or  acetate salt).

Common salt-forming cations include: Common salt-forming anions (parent acids in parentheses where available) include:
 * Ammonium NH4+
 * Calcium Ca2+
 * Iron Fe2+ and Fe3+
 * Magnesium Mg2+
 * Potassium K+
 * Pyridinium C5H5NH+
 * Quaternary ammonium NR4+
 * Sodium Na+
 * Acetate CH3COO− (acetic acid)
 * Carbonate CO32− (carbonic acid)
 * Chloride Cl− (hydrochloric acid)
 * Citrate HOC(COO−)(CH2COO−)2 (citric acid)
 * Cyanide C≡N− (hydrocyanic acid)
 * Fluoride F− (hydrofluoric acid)
 * Nitrate NO3− (nitric acid)
 * Nitrite NO2− (nitrous acid)
 * Phosphate PO43− (phosphoric acid)
 * Sulfate SO42− (sulfuric acid)